1. Field of the Invention
The present invention relates to a sealing and packaging device, wherein respective individual trays disposed at equidistant intervals in a column fashion, and a band-shaped cover film for the purpose of covering these respective trays, are conveyed at the same speed on a conveyor line, the film being welded successively to an edge flange portion of each tray, while being stretched by a packaged item provided in a mounded fashion on the tray.
2. Description of the Related Art
For example, if a block of chicken meat is accommodated in a tray, then the block of chicken will inevitably rise up about the level of the tray. Therefore, when the mounded block of chicken is sealed inside the tray by means of a cover film, it is necessary to stretch the film when it is welded to the edge flange portion of the tray.
JP 2004-203485A discloses a sealing and packaging device of the following kind. More specifically, a plurality of trays each accommodating a packaged item in a mounded fashion are conveyed at equidistant intervals by a chain conveyor. At an intermediate point of the conveyance path, a cutaway region is formed and a general frame is provided so as to border the region. This general frame moves reciprocally along side rails. A sealing base frame is provided in the general frame below the conveyance path of the trays, and as a result of the sealing base frame moving upwards and downwards, as well as moving back and forth together with general frame, the sealing base frame performs a box motion at the same speed as the trays, due to the combined action of these two movements. Due to the box motion of the sealing base frame, the trays are lifted up above the conveyor, thereby stretching the band-shaped film by means of the packaged item provided inside the trays, and in this state, the film is welded to the flange of the tray. In other words, the sealing base frame on the under side of the chain conveyor repeats an elliptical or rectangular box motion. To provide a simple description of the state of stretching of the band-shaped film by the packaged item due to the box motion of the sealing base frame, if the horizontal path of the chain conveyor is imagined to be the surface of the sea, then the box motion of the sealing base frame is similar to the motion of a dolphin jumping out above the surface in an arc-shaped path. Therefore, due to the box motion of the sealing base frame, the trays rise up above the path of the chain conveyor in an arc-shape, like a dolphin jumping out of the sea. Consequently, the band-shaped film positioned above the conveyor is pushed and stretched by the packaged item mounded inside each tray, and in this state, the flange of the tray is pressed against the sealer disposed above the general frame, thereby welding the film to the flange at the perimeter edge of the tray.
However, in this packaging device, the flange of the tray is supported from below by the sealing base frame, and the weight of the packaged item inside the tray is supported via the flange. Therefore, problems have arisen in that, when the packaged item accommodated in a mounded fashion in the tray pushes and stretches the film disposed above it, the tray supported by the sealing base frame distorts due to the increased tension in the film, the base of the tray develops fractures, or the flange of the tray supported by the sealing base frame breaks.